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J. Dyn. Sys., Meas., Control. 2018;140(11):111001-111001-13. doi:10.1115/1.4040220.

In this paper, an analysis is applied to a hybrid airship considering the added mass. First, based on the dynamic mesh technology, a computational fluid dynamics (CFD) method is employed to obtain the added mass coefficient matrix. Through a validation process using the 6:1 prolate spheroid, the 6 × 6 added mass matrix of hybrid airship is obtained. After a dynamic modeling, the equations of motion with added mass are developed. Through the linearization based on small perturbation, the linearized longitude model is used to simulate the dynamic response of a trim condition. The take-off and landing performance has been analyzed and affected by the added mass. The result shows an obvious vertical destabilizing trend on the hybrid airship dynamics due to the added mass and the inertial effect has little influence on the vehicle during the take-off and landing.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111002-111002-10. doi:10.1115/1.4040209.

An adaptive discrete-time controller is developed for a class of practical plants when the mathematical model is unknown and the sampling time is nonconstant or unfixed. The data-driven model is established by the set of plant's input–output data under the pseudo-partial derivative (PPD) which represents the change of output with respect to the change of control effort. The multi-input fuzzy rule emulated network (MiFREN) is utilized to estimate PPD with an online-learning phase to tune all adjustable parameters of MiFREN with the convergence analysis. The proposed control law is developed by the discrete-time sliding mode control (DSMC), and the time-varying band is established according to the unfixed sampling time and unknown boundaries of disturbances and uncertainties. The prototype of direct current-motor current control with uncontrolled-sampling time is constructed to validate the performance of the proposed controller.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111003-111003-13. doi:10.1115/1.4040217.

Lifting up a cage with miners via a mining cable causes axial vibrations of the cable. These vibration dynamics can be described by a coupled wave partial differential equation-ordinary differential equation (PDE-ODE) system with a Neumann interconnection on a time-varying spatial domain. Such a system is actuated not at the moving cage boundary, but at a separate fixed boundary where a hydraulic actuator acts on a floating sheave. In this paper, an observer-based output-feedback control law for the suppression of the axial vibration in the varying-length mining cable is designed by the backstepping method. The control law is obtained through the estimated distributed vibration displacements constructed via available boundary measurements. The exponential stability of the closed-loop system with the output-feedback control law is shown by Lyapunov analysis. The performance of the proposed controller is investigated via numerical simulation, which illustrates the effective vibration suppression with the fast convergence of the observer error.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111004-111004-8. doi:10.1115/1.4040221.

NOx sensor-based state estimations for urea-based selective catalytic reduction (SCR) systems have attracted much attention in the past several years because of their significant importance in achieving high NOx conversion efficiency and low ammonia slip at low operation cost. Most of the existing SCR state estimation techniques require sophisticated design processes and significant tuning efforts, which may prevent them from widespread applications to production urea-SCR systems. In addition, the existing SCR state observers may not be able to achieve fast and accurate estimations due to the corresponding slow estimation error dynamics. The purpose of this study was to design a straightforward and effective NOx sensor-based SCR state estimation algorithm for decoupling post-SCR NOx sensor signals (NOx concentration, ammonia concentration), and for estimating ammonia coverage ratio of the urea-SCR systems. A singular-perturbation-based approach was applied to attain the reduced-order SCR model by decoupling the fast NO and NH3 concentration dynamic models from the slow ammonia coverage ratio dynamics model. Based on the reduced-order model, a direct algebraic approach (DAA)-Newton observer was proposed for estimating ammonia coverage ratio. The achieved ammonia coverage ratio estimation was applied to estimate the post-SCR NOx and NH3 concentrations. Simulation verification results under US06 cycle proved the effectiveness of the proposed method in accurately estimating the aforementioned key SCR states. The proposed observer can potentially be popularly applied to the production SCR systems for the advanced SCR control systems and on-board diagnostics.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111005-111005-8. doi:10.1115/1.4040218.

In this paper, we study nonlinear robust stabilization of roll channel of a pursuit using the sum of squares (SOS) technique. Roll control is a fundamental part of flight control for every pursuit. A nonlinear state feedback controller is designed based on a new stability criterion which can be viewed as a dual to Lyapunov's second theorem. This criterion has a convexity property, which is used for controller design with convex optimization. Furthermore, using generalized S-procedure lemma robustness of the controller is guaranteed. The performance of the proposed method for roll autopilot is verified via numerical simulations.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111006-111006-10. doi:10.1115/1.4040325.

Hydraulic presses are widely applied in various forming processes to manufacture products with complex shapes, however, they are energy-intensive. In order to lower the energy consumption, a variable-speed variable-displacement pump unit (SVVDP) was developed for hydraulic presses, where the flow rate required by the press in a forming process can be realized by changing the motor rotating speed and the pump displacement simultaneously. A theoretical model was built to reveal the energy dissipation behavior of the drive unit, which shows that the energy efficiency of the drive unit can be optimized by varying the rotating speed of the motor under a variety of load conditions. An experimental platform with a SVVDP was established to find the optimum rotating speed and the corresponding displacement in different load conditions, and experimental results verified the improved energy efficiency of the SVVDP compared with that of the commonly used single variable drive unit. By employing the strategy that the determined optimum rotating speeds in different load conditions were preset as recommended values for the drive unit working in different operations, the proposed drive unit was applied to a press completing a forming process and the results indicate significant energy saving potentials.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111007-111007-10. doi:10.1115/1.4040296.

This paper discusses the averaging, control authority, and vibrational control of mechanical control-affine systems with high-frequency, high-amplitude inputs. The inputs have different frequencies of the same order. This work is an extension of the existing averaging method for high-frequency mechanical systems with single-frequency inputs. Vibrational control authority of mechanical control-affine systems is introduced, and the effects of inputs' waveform and frequency on vibrational control authority are investigated. The results show that, in general, using multifrequency inputs may result in lower control authority of mechanical systems compared to single-frequency inputs, especially when using harmonic inputs. The results on vibrational control authority of the systems with multifrequency inputs are demonstrated using vibrational control of a horizontal pendulum with two inputs. This paper also discusses the averaging of multiple-time-scale control systems.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111008-111008-10. doi:10.1115/1.4040251.

Efficient control of a gas metal arc welding (GMAW) process enables one to obtain high quality products as a consequence of achieving a high quality weld. Although control of the droplet detachment frequency in the welding process would play a great role in improving the welding quality, measuring this variable is difficult and expensive. In this paper, we attempt to control the frequency of droplet detachments without directly measuring it. To this end, we utilize the hybrid property of the GMAW process to indirectly control the frequency. Specifically, a mixed logical dynamical (MLD) model is obtained by considering the hybrid act of the process during droplet detachment. Then, a nonlinear model predictive controller with variable control and prediction horizons is designed incorporating the hybrid behavior of the process. The controller regulates the droplet detachment frequency without measuring this variable directly. Computer simulation results show that the proposed controller leads to a higher quality weld compared to the present approaches.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111009-111009-11. doi:10.1115/1.4040219.

Hybrid electric vehicle (HEV) energy management strategies usually ignore the effects from dynamics of internal combustion engines (ICEs). They usually rely on steady-state maps to determine the required ICE torque and energy conversion efficiency. It is important to investigate how ignoring these dynamics influences energy consumption in HEVs. This shortcoming is addressed in this paper by studying effects of engine and clutch dynamics on a parallel HEV control strategy for torque split. To this end, a detailed HEV model including clutch and ICE dynamic models is utilized in this study. Transient and steady-state experiments are used to verify the fidelity of the dynamic ICE model. The HEV model is used as a testbed to implement the torque split control strategy. Based on the simulation results, the ICE and clutch dynamics in the HEV can degrade the control strategy performance during the vehicle transient periods of operation by around 8% in urban dynamometer driving schedule (UDDS) drive cycle. Conventional torque split control strategies in HEVs often overlook this fuel penalty. A new model predictive torque split control strategy is designed that incorporates effects of the studied powertrain dynamics. Results show that the new energy management control strategy can improve the HEV total energy consumption by more than 4% for UDDS drive cycle.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111010-111010-8. doi:10.1115/1.4040326.

This paper presents a novel configuration of flight vehicle with moving mass control. We focus on the development of the proposed control mechanism and investigate the feasibility of an equivalent experimental setup. First, the effect of the moving mass parameters on the control authority is investigated. Then, a control law based on immersion and invariance (I&I) theory is presented for the moving mass control system. In the design process, we select a first-order target system to reduce the difficulty of controller design. To deal with the coupling caused by the additional inertia moment, which is generated by the motion of the moving mass, the extended state observer (ESO) is designed. The proposed adaptive controller is simulated and tested on the experimental setup. Finally, the simulation results validate the quality of the proposed adaptive controller, which ensures a good performance in the novel configuration with internal moving mass.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111011-111011-12. doi:10.1115/1.4040216.

Spatially dependent transfer functions for web span lateral dynamics which provide web lateral position and slope as outputs at any location in the web span are derived in this paper. The proposed approach overcomes one of the key limitations of the existing methods which provide web lateral position only on the rollers. The approach relies on taking the Laplace transform with respect to the temporal variable of both the web span lateral governing equation and the boundary conditions on the rollers, and solving the resulting equations. A general web span lateral transfer function, which is an explicit function of the spatial position along the span, is obtained first followed by its application to common guide configurations. The approach also significantly simplifies the consideration of shear (relevant to short spans), in addition to bending, which has been found to be difficult to handle in past studies. We first develop spatially dependent lateral transfer functions by considering only bending which is relevant to most web handling situations, and then add shear to the formulation and develop spatially dependent lateral transfer functions that include both bending and shear. Results from model simulations and pertinent discussions are provided. The spatially dependent transfer functions derived in this paper are a significant improvement over existing lateral transfer functions and provide mechanisms to analyze web lateral behavior within spans, study propagation of lateral disturbances, and aid in the development of closed-loop lateral control systems in emerging applications that require precise lateral positioning of the web.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111012-111012-9. doi:10.1115/1.4040420.

This paper proposes an iterative linear matrix inequality (LMI) method for tuning the parameters of multi-input multi-output (MIMO) proportional–integral–derivative (PID) controllers. The proposed method calculates the parameters of controller such that the singular values (SVs) of the sensitivity function are shaped according to the given weight function. For this purpose, first using bounded real lemma (BRL), this problem is represented as a bilinear matrix inequality (BMI) where one of the matrix variables is the variable of Lyapunov equation and the other is structured and contains the matrices of the state-space representation of the controller. This BMI is solved approximately using a novel iterative procedure which linearizes the BMI around an initial solution to arrive at an LMI. The point around which the BMI is linearized is updated automatically at each iteration and the linearized BMI has the nice property that it is obtained by minimizing the amplitude of nonconvex terms.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111013-111013-10. doi:10.1115/1.4040295.

This paper considers a novel coupled state-dependent Riccati equation (SDRE) approach for systematically designing nonlinear quadratic regulator (NLQR) and H control of mechatronics systems. The state-dependent feedback control solutions can be obtained by solving a pair of coupled SDREs, guaranteeing nonlinear quadratic optimality with inherent stability property in combination with robust L2 type of disturbance reduction. The derivation of this control strategy is based on Nash's game theory. Both finite and infinite horizon control problems are discussed. An under-actuated robotic system, Furuta rotary pendulum, is used to examine the effectiveness and robustness of this novel nonlinear control approach.

Commentary by Dr. Valentin Fuster
J. Dyn. Sys., Meas., Control. 2018;140(11):111014-111014-9. doi:10.1115/1.4040328.

The present study is focused on the construction of a well-performing pilot controlled proportional flow valve with internal displacement-flow feedback. A novel control strategy for the valve is proposed in which the flow rate through the valve is directly controlled. The linear mathematical model for the valve is established and a fuzzy proportional–integral–derivative (PID) controller is designed for the flow control. In order to obtain the flow rate used as feedback rapidly and accurately in real-time, back propagation neural network (BPNN) is employed to predict the flow rate through the valve with the pressure drop through the main orifice and main valve opening, and the predicted value is used as the feedback. Both simulation and experimental results show that the predicted value obtained by BPNN is reliable and available for the feedback. The proposed control strategy is effective with which the flow rate through the valve remains almost constant when the pressure drop through the main orifice increases and the valve can be applied to the conditions where the independence of flow rate and load is required. For the valve with the proposed control strategy, the nonlinearity is less than 5.3%, the hysteresis is less than 4.2%, and the bandwidth is about 16 Hz. The static and dynamic characteristics are reasonable and acceptable.

Commentary by Dr. Valentin Fuster

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